Magnetic chains on s-wave superconductors evoke so-called Shiba bands inside the gap of the
substrate. If these bands experience sufficiently strong spin-orbit couplings and overlap with the
Fermi energy, a topologically nontrivial minigap can open up which may protect zero energy
Majorana bound states localized at the chains two ends. We study artificial spin chains, built atom-
by-atom [1], with respect to such phenomena. By variation of substrate and adatom species and
interatomic distances in the chain [2-5], we adjust the energies of the multi-orbital Yu-Shiba-Rusinov
states induced by the adatoms [2,3], their hybridizations [4], as well as the chains’ spin structures [5].
This enables us to tailor the multi-orbital Shiba bands formed by hybridizing Yu-Shiba-Rusinov states
such that topologically nontrivial minigaps open [6] and precursors of Majorana bound states appear
[7]. Due to a narrow energetical width of the topological minigaps in the systems realized to date, the
two components of the Majorana precursors from the two chain ends strongly hybridize, such that a
desired protection by the topological minigap is not yet achieved. Here, I will review our work,
present our most recent strategies in order to increase the width of the topological minigap [8-11],
and show experimental methods we developed to decide on the topologically trivial or non-trivial
nature of close-to-zero-energy end states [12]. I will also present very recent results in coupling spins
on superconducting surfaces to quantum dots [13].
I acknowledge funding by the German Research Foundation (DFG) via the Cluster of Excellence
’Advanced Imaging of Matter’ (EXC 2056-project ID 390715994).
References